Variables affecting proper system grounding for radiofrequency ablation inan animal model

PURPOSE: The authors sought to determine which factors contribute to excess ive thermal deposition and burns at the grounding pad site after high-curre nt percutaneous, image-guided radiofrequency (RF) ablation, MATERIALS AND METHODS: Radiofrequency (1,000-2,000 mA) was applied for 10 m inutes with use of an internally-cooled electrode placed into in vivo pig l ivers (n = 88), In separate experiments, the number of pads (1, 2, or 4), o rientation of pads (horizontal, vertical, or diagonal), and distance betwee n the pads and the electrode (10-50 cm) of mesh or foil grounding pads (12. 5 x 8 cm; 100 cm(2)) were varied. Thermistors measured skin surface tempera tures during ablation, Pathologic analysis of skin changes was performed. RESULTS: Temperature elevations at the grounding pad were observed for ever y trial, with a temperature elevation greater than or equal to 12 degrees C (as high as 45 degrees C) observed in 60 of 88 trials (68.2%). Temperature s at the grounding site pad were dependent on all variables studied, includ ing the grounding pad surface area, the amount of current deposited in the liver, the orientation of the pad, and the pad's distance from the electrod e. Second-degree burns were seen with temperatures exceeding 47 degrees C a nd third-degree burns were observed when a temperature greater than or equa l to 52 degrees C was noted. For a given set of RF parameters, reduced heat ing was observed for trials in which foil grounding pads were used (P < .00 1), Grounding pad burns did not occur at 2,000 mA (maximum generator output ) when four foil pads were placed horizontally greater than or equal to 25 cm from the electrode. CONCLUSIONS: High-current RF ablation can induce severe burns at the ground ing pad site if inadequate precautions are taken. To minimize the risk of b urns, multiple large-surface-area foil pads should be placed on well-prepar ed skin and oriented with the longest surface edge facing the RF electrode.